Transparent plastic materials



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' TRANSPARENT PLASTIC MATERIALS 7 Filed Jan. '28, 1939 V 4..05/ (I 7 M4 a 7 mvsmo BJ' RN AND RsON 'WORNEYS Patented Apr. 21, 1942 TRANSPARENT PLASTIC MATERIALS Bjorn Andersen, Maplewood, N. 1., assignor, by mesne assignments, to Celanesc Corporation of America, a corporation of Delaware Application January 28, 1939, Serial No. 253,251

6 Claims. (01. 2-14) This invention relates to the production of transparent plastic materials or improved properties, and relates more particularly to the production of a non-fogging type of transparent plastic material.

An object of this invention is to provide a transparent plastic material which is not susceptible to fogging or sweating when exposed to moistureladen atmosphere or at low temperatures conducive to moisturecondensation.

Another object of this invention is the provision of a transparent plastic material suitable for use as lenses in goggles and eye glasses, as Windshields in automobiles, airplanes, military tanks, and as transparent containers for moisture containing substances, etc. A further object of this invention is to provide a transparent plastic material having a moisture-absorptive surface which prevents fogging and which is impervious to moisture, gases and the like.

A specific object of this invention is the provision of an improved transparent plastic material which is suitable for use as lenses or eyepieces in gas masks.

Other objects of this invention will appear from the following detailed description.

Although as indicated above the transparent plastic material of the present invention may satisfactorily be used in all places where fogging or sweating of glass or glass substitutes is objectionable, the present invention will be described in connection with its use in gas masks where the provision of a fog-proof or sweatproof eyepiece is of the utmost importance.

To overcome in some measure the fogging or sweating that takes place on glass, ordinarily used in gas masks, attempts have hitherto been made to utilize a thin sheet of gelatin or other moisture absorptive transparent medium on the mospheric conditions, the gelatin swells, becoming sticky, wrinkled and putrescent thereby necessitating frequent replacements. Such -replacements may be made in goggles and'the like but, as will readily be appreciated, it may be extremely hazardous to make a replacement of the gelatin inserts in a gas mask when worn in a gas-laden atmosphere, for example. Ii. these replacements of the inserts are not made when necessary, 1. e., when the inserts are swollen, tacky, wrinkled or buckled, the vision is distorted making the gas mask useless for its designed purposes. Furthermore, the gelatin inserts whe shrink and crack so that they do not fit properly when attached to the lenses nor do they afford the clear vision which is required.

The inherent disadvantages of the gelatin inserts have led investigators to try other expedients to prevent the fogging or sweating of glass lenses. For instance, attempts have been made to use on the lenses of the gas masks chemical compositions found on the market for spraying on to glass Windshields to prevent frosting, water condensation or sweat, etc. These chemical compositions were not satisfactory for use on the lenses of a gas mask since it was not always convenient to take oil the gas mask and apply these compositions. For example, a gas mask could not with safety be taken ofi in a poisonous gas-laden atmosphere for the purpose of applying to the lenses a fog-preventing composition. Furthermore, some of these chemical compositions are irritating to the eyes when applied to lenses confined within a closed space such as in a gas mask or tight fitting goggles. Other objections are their water-solubility resulting in the such plastic materials were all made more or" less water-insoluble to minimize moisture ab sorption. These plastic materials could, or

course, be made more porous and sponge-like pair vision and permit gases to seep therethrough,

prohibiting their use as lenses in gas masks.'

In accordance with my invention I produce a transparent plastic material having non-fogging and non-sweating characteristics, which transparent plastic material retains its non-porous character, by treating one or both surfaces only of a derivative of'cellulose sheet leaving the in her portion or core thereof -in a substantially unaflected condition. Such a sheet is substantially impervious to both moisture and gas and has a layer, on one or both surfaces thereof,-

which is water-absorptive. I

. In the accompanying drawing wherein the preferred embodiments of my invention are shown,

stored in extremely dry warm places tend to Figure 1 is a front view of a mask employings lens made from thesheet material of my invensuch as soap, sodium acetate, sodium oleate, tion, thlocyanates, borax, alcohol, glycol and polyglycol Figure 2 is a front view of a pair of goggles or their derivatives such as methyl glycol, etc., the lenses of which are made from my improved may be added to the saponifying bath.

sheet material, and The sheet materials used in accordance with Figure 3 is a showing on an enlarged scale of this invention may contain, besides the cellulose a cross-section of the material of my invention. ester, effect materials for modifying the proper- Referring to Figure l of the drawing, the mask ties of said sheet materials, such as plasticizers, in which my invention is embodied is generally fillers, dyes or lakes, fire retardants, etc. For inindicated by reference numeral 5 and is shown stance, the sheet material may contain about 5 held in position on the head of the wearer by to 30 or more parts of plasticizer which may he means of straps 6. The mask comprises a faceany suitable one for the particular cellulose ester piece I, made of rubber or other suitable flexible employed. The plasticizers may be any of the and gas-impervious material, and has mounted high boiling solvents or softening agents as, for in the lower portion thereof an air-purifying 1:, example, the aryl sulphonamides such as para canister 8, the upper portion thereof being proethyl toluol sulphonamide, the alkyl phthalates vided with an eyepiece or lens 9. Although a such as dimethyl phthalate, the dialkyl tartrates single large eyepiece is shown, it will be undersuch as dibutyl tartrate, the alkoxy esters of stood that two eyepieces, one for each eye, may polybasic organic acids such as dimethoxy ethyl be used if desired. The goggles ll shown in phthalate, the polybasic acid esters of the mono Figure 2 have set therein in any suitable manalkyl ethers of polyhydric alcohols such as nereyeple l ma eo the n n-f ea ns d nondiethylene glycol ethyl ether ester of phthalic sweating sheet material of my invention. These acid, the alkyl esters of phosphoric acid such as eyep y 9-150 represent inserts or linings of triethyl glycol phosphate, the aryl esters of phosthe non-fogging plastic sheeting used in conjuncphoric acid such as triphenyl phosphate, tricresyl tion with the glass lenses as already described in phosphate, the mixed alkyl and aryl phosphates,

the case of gelatin inserts. and camphor. A mixture of any of the foregoing In accordance with this invention I produce plasticizers maybeemployedif desired. The fire sheet material, which is not susceptible to fogretardants which may be employed in the celluging or sweating when exposed to moisture laden lose ester sheet material may be tricresyl phosatmosphere, for use wherever such non-fogging phate, triphenyl phosphate, chlorinated naphor non-sweating material is desirable, by superthalenes, chlorinated diphenyls, compounds conficial saponification, hydrolyzing or de-esterificataining bromine and other like fire retardants tion of sheet material comprising esters of celluknown to be compatible with the cellulose ester lose such as cellulose nitrate, cellulose formate. employed. The fire retardants may be added to cellulose propionate, cellulose aceto propionate. the sheet material in a quantity of about 15 or cellulose butyrat, cellulose aceto butyrate and more parts by weight. If desired water soluble particularly cellulose acetate. Such superficial plasticizers and/or fire retardants may be used saponification is indicated in Figure 3 where to some extent as, for example, to secure a there is shown a sheet l3 saponified superficially greater depth of porosity. at the surfaces H. In accordance with this in- While any of the foregoing saponifying agents vention either one or both of the surfaces may be may be used in making the sheet material of saponified. In order to obtain sheets which are my invention, I prefer to use an aqueous solution perfectly fiat and free from distortion, knife of ammonia. In the preferred process of treatlines," etc. it is preferable to heat press and ing the cellulose acetate sheet material the sheets polish the sheets before and after treatment with which may vary in thickness from about 0.001 to the saponifying agent. 0.100 of an inch or more are first cleaned and Superficial saponificationgf thg cellulgse gstgr then polished in the usual manner between heatslieet'fmatEfiaFmaybe fiected in convenient ed polishing plates. These sheets are then immanner such arty treatment lrilanjilkalinbath mersed for a period 01' from 2 to 6 hours, de- -or by padding or otherwise fiiecha nicallyiini; pending on the thickness, in a saponifying bath eregfiaang the sheet material with the requisite containing ammonia in a concentration of about quantity of saponifying age ri 15 to 20%, at a temperature between 60 to 75 The alkaline bath used for superficially saponi- F., preferably 65 F. .If the temperature exceeds fying the celluloseester sheet material may be 75 F. an undesirable distortion of the sheet either of low concentration or high concentration material may take place. After the sheets are depending on the temperature and duration of taken from the bath they are washed in running treatment; If an alkaline solution of low conwater at a temperature of to 75 F., preferably centration is used higher temperatures may be F., for from 20 to300 hours depending upon employed in the process, whereas if alkaline solu- Go the thickness of the sheet being treated. In ortrans of high concentrations are employed low -der to prevent discoloration of the sheet mate- 'temperatures of treatment are used. If a solurial it is preferable to exclude air from the tion of intermediate concentration is employed, sheets until all of the ammonia and degraded intermediate temperatures of treatment should products have been removed by washing or scrubbe used. The saponifying bath may contain any 65 bing, The surfaces of the sheets are then dried suitable alkali or alkaline salt for producing hythoroughly by wiping with chamois and by stordroxyl ions in aqueous solution. The alkalies ing the sheets at room temperature between tiswhich may be used are sodium hydroxide, potassue" lined falulah boards for a period of 3 to slum hydroxide or ammonia. Examples of 4 hours to 3 days depending ,on the thickness of alkalinesalts are sodium or potassium carbonthe sheet employed. For example, sheets of a atesfsodimn potassium, or ammonium sulphide thickness of 0.005 to 0.010 of an inch are dried or hydrdsulphide, sodium or.'potassium silicate at room temperature for 3 to 4 hours, whereas a'ndtri-sodium phosphate. In order to promote sheets having a thickness of 0.060 of an.inch intense su face saponification of the cellulose are preferably dried for 24 hours at room temester sheet material salts or modifying agents perature between the boards, then are transferred to dry pads and further dried for 24 hours at 120 F. and then 24 hours at 140 F. when the sheets are thoroughly dried they are flattened between polishing plates in a Dre-heated press for about 20 minutes at 50 to 150, preferably 125, pounds of steam under from 500 to 1500, preferably 1250, pounds of hydraulic pressure per square inch. This removes any surface irregularities, distortions, knife lines, etc. The p01- ished sheets are then readyjor use.

As will appear from the following tables, the cellulose ester sheets treated in accordance with this invention have ph sical characteristics which are quite different from those of the ontreated sheet.

The chemical formula of the sheets tested is cellulose acetate 100 parts by weight and dimethoxy ethyl phthalate (plasticizer) 30 parts by weight. This composition is, however, only illustrative.

(A) Untreated sheet Thickness --thousandths oi inch. Fog resistance seconds 2 2 2 Tensile strength. in pounds per sq. in;

A. Yield point 6,160 4,825 5,260

B. Break point" 6,150 5,860 Elongation .7 35.5 32.1

ardness .66 6.34 6.74 Moisture absorptw 3.94 4.05 4.50 Water shrinkage .717 .387 Heat loss 3 17 2.84 1.64

(B) Treated sheet (Non-jogging) Thickness tbousandths of inch 5 l0 2 Fog resistance.1i seconds 140 Tensiestren t in on s rsq. in.:

A. Yield poinng 9,850 8,850 7.300

B. Bleak point 9 8,850 7,560 Elongation percent... 10 2 16 30 Hardness 10.6 9.13 lgoisturle alllalsorption. i 074 7.1;? 5.2303

aiers r' e percen Heat lossnni .258 .211

In the tables the figures for "Fog resistance were obtained by first preconditioning the sample of the sheet to be tested for one hour at 80 F. and 50% relative humidity. The sheet was then placed flat over the mouth of a one quart Mason jar containing one pint of water at F., the jar being in turn placed over a newspaper. The time in seconds was noted when fogging first began to appear and the newsprint become illegible. By this test, treated or nonfogging plastic sheeting is fog resistant for not less than 50 seconds, usually from 90 to seconds, whereas untreated plastic sheeting and glass will fog in two seconds or less. The-figures for hardness are expressed as Brinell hardness in kilograms per square millimeter with a 3.5 millimeter ball, 10 kilogram load, 1 minute.

The moisture absorption figures were obtained by conditioning the sheet material for 24 hours at zero percentage relative humidity, and noting lulose acetate sheet material it decreases as the thickness increases. The treated material is moreover decidedly harder and more scratch-resisting than the untreated sheet material. This is probably due to the case hardening effect of the saponifying. treatment and the absence on the surface of any substance such as a plasticizer. Indeed, cellulose acetate sheets treated in this manner appear to approximate the good mechanical properties of the well known product, Celluloid, such as resiliency and stiffness without brittleness, which are so much desired in the plastics industry. The light transmission of the treated. sheet material is over 90% of white light which is practically unaffected by long exposure to sun or ultra violet light. For example, one hundred hours exposure in a standard Fadeometer testing machine caused only a slight bleaching of color with no apparent effect on light transmission.

The tables also show that the moisture absorption is very high in the treated plasticized cellulose acetate sheet material as compared with the untreated plasticized cellulose acetate sheet materialJwhile the water shrinkage is less. .A--

marked difierence will also be noted in the weight loss at elevated temperatures, the untreated plas ticized cellulose acetate sheet material losing appreciably after 3 days at 70 C. The case-hardening saponified layer in the treated sheet material acts as a seal and prevents further volatility of the plasticizer from the core of the sheet material. This is a very significant finding. Its benefits are appreciated in the case of printing cellulose acetate sheets and subsequently polishing same. The difilculties of ink transfer as brought out in U. S. Patent No. 1,931,485 are considerably diminished. Due to the porous surface the ink is more readily absorbed. In polishing the sheet any tendency of the plasticizer to exude is offset by this superficial absorption. Indeed, the treated sheets may be-readily marked with ordinary ink and pen, and for this reason are very suitable for tracing cloth purposes. This ease of printing is utilized to advantage in marking or printing the non-fogging material, particularly when it is used for packaging purposes.

the gain in weight after 48 hours at 90% relative humidity. To obtain the figures for. water,

I treated sheet material of plasticized cellulose acetate is remarkably stronger than the untreated plasticized cellulose acetate although the per-. centage of elongation is less. The latter, how- 'ever, increases with the thickness of the sheet material whereas in the untreated plasticized celwith cements such as gelatin, etc. The exudation of plasticizer .on the surface of the sheet forming ancily-skin interfering with proper adhesion to the glass or gelatincoating is appreciably mini mized. This quality is also of material aid when it is desired to make anti-fogging, shatterproof glass lenses, wlndshields, etc., where one or both sides otthe glass has a treated sheet of cellulose ester laminated thereto. The toughness andresiliency of the treated plastic sheeting, compared with an untreated sheet, make for added safety. If desired a roll of cellulose acetate film may have one or both sides saponified or deesterified sufficiently so that a thin coating or substratum of gelatin may be effectively applied. After the film is thus "subbed" say in continuous lengths, a thicker adhesive layer of glue, gelatin. gum arabic, casein, sodium silicate, egg albumin, dextrin, glyceryl or glycol boriborate resins, etc., may be subsequently applied so that the final, dried coated film or sheeting may be stuck to a variety of surfaces such as glass, wood, metal, paper, etc., by the mere application of water as in sticking of a postage stamp. In the past it has been quite difiicult to apply gelatin coatings, even though extremely thin, directly to plasticized cellulose acetate materials, for example, in motion picture and X-ray film, where a heavier coating of light sensitive gelatin emulsions is usually applied over the thin gelatin substratum. This difficulty in securing proper anchorage of the gelatin to the surface of the film is generally attributed to the incompatibility of the oily, water-insoluble or hydrophobic plasticizer in or on the film with a hydrophilic colloid such as gelatin. The saponiflcation of the cellulose ester and plasticizer results in a porous, water absorptive layer making possible more effective gelatin substrating. Ordinary glued paper labels may also be readily stuck to the surface of the non-fogging sheet by mere application of moisture. This feature is also quite desirable for packaging material.

While this invention thus finds exceedingly useful applications in many fields, the physical properties of the sheet material treated in accordance with this invention makes the same eminently suitable for use where non-fogging, transparent sheet material is desired. For example, when the sheet material of this invention is used as lenses in gas masks and goggles. or as inserts in combination with glass as previously described. or as containers or windows in food cartons, the said material will not fog or sweat due to the condensation moisture thereon, such as may be induced by exposure to low outside temperatures. This feature, as indicated above, is due to the porous and moisture absorptive character of the surface of the sheet material. No droplets of the moisture (fog) will appear on the surface of the sheet to mar the transparency thereof. Moreover, the treated material will not wrinkle or become sticky and distorted in use due to shrinkage or swelling, but will remain strong. flexible, non-tacky, non-moldy, clear and durable. Treated material will also exhibit less static than untreated material which is highly desirable in the case of packaging material. The treated surface is also more resistant to spotting by solvents such as acetone, alcohol, etc.

If desired, the treated sheets or films may be suitably composited or laminated to one or both sides of other plastic materials, such as those made of cellulose derivatives, synthetic resins such as Vinyloid, Lucite, styrol, condensation products of urea-formaldehyde,phenol-formaldehyde, glycerol-phthalic anhydride, etc.

While this invention has been described primarily with reference to the treatment of sheets,

it is obvious that the cellulose ester material bein treated may be in any other form such as a molded article of irregular shape and thickness,

for example, threaded lens tops for flashlights are generally made by the so called injection molding of cellulose acetate. Such a finished molded article may be subjected to a saponiflcafo gin or sweating. said eyepieces being made of sheet material containing an ester of cellulose, the inner surface of the eyepieces, which is exposed to said moist warm atmosphere, being saponified so that it is capable of absorbing moisture and the sheet material as a whole being resistant to the penetration of water and gases.

2. Gas masks, goggles and the like having eyepieces, adapted when in use to be exposed on the inner side to a moist warm atmosphere and on the outer side to a colder atmosphere without fogging or sweating, said eyepieces being made of sheet material containing cellulose acetate, the inner surface of the eyepieces, which is exposed to said moist warm atmosphere, being saponifled so that it is capable of absorbing moisture and the sheet material as a whole being resistant to the penetration of water and gases.

3. Gas masks, goggles and the like having eyepieces, adapted when in use to be exposed on the inner side to a moist warm atmosphere and on the outer side to a colder atmosphere without fo ing or sweating, said eyepieces being made of sheet material containing an ester of cellulose, said sheet material being saponified on its inner surface, which is exposed to said moist warm atmosphere, and substantially unsaponified throughout the greater portion of its thickness. whereby the sheet material as a whole is resistant to the penetration of water and gases.

4. Gas masks, goggles and the like having eyepieces, adapted when in use to be exposed on the inner side to a moist warm atmosphere and on the outer side to a colder atmosphere without fogging or sweating, said eyepieces being made of sheet material containing cellulose acetate, said sheet material being saponified on its inner surface. which is exposed to said moist warm atmosphere, and substantially unsaponifled throughout the greater portion of its thickness, whereby the sheet material as a whole is resistant to the penetration of water and gases.

5. Gas masks, goggles and the like having eyepieces, adapted when in use to be exposed on the inner side to a moist warm atmosphere and on the outer side to a colder atmosphere without fog i g or sweating, said eyepieces being made of laminated sheet material the laminae of which are sheet glass and a cellulose ester material, the lamina on the inner side of said eyepiece, which is exposed to said moist warm atmosphere, comprising cellulose ester material the exposed surface of which is saponified so that it is capable of absorbing moisture, and the laminated material as a whole being impervious to water and gases.

6. Gas masks, goggles and the like having eyepieces. adapted when in use to be exposed on the of absorbing moisture, and the laminated material as a whole beingimpervious to water and gases. BJORN ANDERSEN. 

